Tachometer



Dec. 7, 1943. R. o. HELGEBY 2,336,172

TAG HOMETER Filed Oct. 20, 1941 I attorneys 3nventor Patented Dec. 7, 1943 TACHOMETER Ralph 0. Helgeby, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application October 20, 1941, Serial No. 415,703

1 Claim.

The accompanying drawing shows such an instrument.

Figure 1 is a longitudinal section. Figure 2 is a section on line 2--2 of Figure 1. Figure 3 is a section on line 3-3 of Figure 1. Figure 4 is a view in elevation of the assembled instrument.

Referring to the drawing, numerals 5 and I represent two cup-shaped casing members made from inexpensive material. Member 5 has a cylindrical wall 9 extending from a partly spheriical end ll. Into an opening of this end is fitted a plug [3. At the end of wall 9 there is formed a radial flange l5. Wall 9 has an opening I! internally covered by a transparent plate of suitable material marked IS.

The tachometer of that well-known kind having a rotatable permanent magnet, a fixed field cup and a rotatable speed cup. The field cup is marked 2|. It has a radial flange 23. The base of the field cup has at an aperture serving as'a bearing for the spindle 21 of the speed cup 29. To register with opening ll of the casing wall 9 is an opening 8 in the field cup. There are suitable indicia on the speed cup as shown by Figure 4 to cooperate with a lug on the field cup wall wherebyreadings are determined. To return the speed cup to its zero reading, there is a hair spring 3| anchored at one end to a tongue 33 bent up from the field cup. At its other end the hair spring is attached to a washer 35 carried by the spindle. This washer serves also to limit axial movement of the speed cup and spindle.

The rotation of the speed cup is efiected by eddy currents produced by the rotation oi a permanent magnet at a rate corresponding to the rate 01 rotation of the shaft the speed of which is to be determined. To that end casing member I is press litted to a hub or shalt bearing 31 within WlllUIl rotates sna'it 33. To provide anti-frictional rotation, the hub has a radial opening 4| containing an oil saturated wick l3 and a plug closes the opening. Snait 33 is recessed axially to receive hoh-rotatably a drivesplndle H to which is fitted a knurled shalt engaging tip 49, the latter to engage a suitable recess 5| in shaft 53 which is the shaft the speed of which is to be determined. Shoulder 55 and spacer 51 retain shaft 39 from axial movement in the hub. Shaft 39 is enlarged as at 59 and its end is reduced as at 6| to form a shoulder 63 against which is seated a permanent magnet 65 which may be of U-shape. The end of shaft 31 is apertured as at 61 and provided with a bearing 69 for the speed cup spindle. A temperature compensator may be used. One is shown at H positioned adjacent the magnet. The magnet and compensator are held in position by peening over the metal around the Opening 61.

After the field cup with the speed cup and its spindle are assembled as shown in Figure 1, with the flange of the field cup against the flange of easing member 5, the casing member 1 with hub 31 and the magnet carrying shaft 39 is placed in position, the speed cup spindle being received with hearing 69. Parts of the periphery of casing member 5 are then crimped over the adjacent part of easing member I to complete the assem- D13.

With tachometer completely assembled, the magnet may then be magnetized to some degree of success. It is then calibrated by a process 01 demagnetiz'iiig and ii necessary the cap l3 may be removed and a final correction made by ad- Justing the hair spring at 33.

An instrument as described will be quite inexpensive. it is light, small and can be easily carried about. it will be quite accurate and will supply the demand ior a reasonably priced serviceaoie tachometer.

.L claim:

a tachometer comprising a shaft, a magnet carried thereby, a speed cup surrounding said magnet, a spindle carrying said speed cup, 9. held cup having a circular bottom wall and a side wall surrounding said speed cup, said speed cup spindle oeing uurnalled in the bottom wall or the hem cu and in the end or said suait, said held cup side wall having a radial nange, a two part casing, 21. ilrst part having a radial nange engaging said held cup mange, the second casing part having a radial hange engaging the opposite race 01 we 1161a cup nalige, one UL 53.111 03.5111

lianges having 411 eklidnutu POL'HUD CIH-LLPGQ. over LL18 hange 01; but 051161 part BO 11010. SHAH oiid casing part having an axially apertured hub secured thereto, said magnet carrying shalt being Jouriiaiied iii said hub and extended outwardly thereiroui, a tapered tip on said shalt extension loi contact with a i'utatauie iiieihuer the speed 01 rotation 01 which is to be determined.

Wu 0. nriL-GEBY. 

